In 1987, E. Yablonovitch of Bell laboratory of the United States and S. John of Princeton University independently put forward the concept of photonic crystal (PhC) respectively in discussion about suppressions of spontaneous radiations and in discussion about localizations of photons. The PhC has a substance structure formed by periodically arranging dielectric materials in a space, and is usually an artificial crystal composed of two or more materials with different dielectric constants.
A PhC has strong and flexible control ability for the light propagation, and has high conduction efficiency for both of the linear transmission and sharp right-angle transmissions. If a line effect is introduced in the PhC architecture for creating a light-guiding channel, called a photonic crystal waveguide (PCW), the waveguide passed through this PhC architecture only has a small loss even at the corner of the right angle (90 degrees). The above mentioned PhC architecture is totally different from the traditional basic optical waveguide having the completely internal reflection, and the effect of the defect-type waveguide is adapted for guiding the photon within the photonic band gap (PBG) to form a new state, and the density of the new state of photon adjacent to transmission mode in the defect-type waveguide is zero. Therefore, the defect-type waveguide is used as a PCW to achieve the transmission mode without the leakage of light, and the PCW is the basic device to form a photonic integrated circuit. The right-angle PCW is improve the integration of optical circuit, so the associated research with respect to the right-angle PCW is very important.